(ShB Spoilers) Didn't Hydaelyn, uh...

[Lurina]

Though Emet-Slech's description of how the sundering worked did not present any conclusion that the person hit by the sundering was actually killed or even considered dead, merely made lesser.

Could you elaborate on this a bit? Emet-Selch explicitly states that the Sundering resulted in everyone losing more or less all their memories of their previous lives, while of course their souls (and possibly bodies?) were also maimed/transformed in the process. Both this and the rejoining are basically processes where the identity of the victim is lost, but the spiritual essence is retained, though changed. I wouldn't dispute that the rejoining is also murder, but what leads you to conceptualize one as death, but not the other?